The present invention relates to a method and an apparatus which enable a multi-gradation display with three or more gradations through use of, for example, a liquid crystal display panel in which each picture element is capable of producing a display with only two gradations.
For providing a multi-gradation display on a liquid crystal display, it is customary in the prior art to employ an arrangement in which an analog picture element signal is supplied from the source side of a thin film transistor to each picture element electrode (a drain electrode) for driving it. The liquid crystal display is usually what is called a row scan type in which picture element electrodes are arranged in a matrix form and are driven row by row for display. In order to display an analog display signal such as a TV signal on the row scan type display, it is necessary to hold each picture element signal in an analog sample hold circuit for each horizontal scanning line of the input TV signal.
On the other hand, a binary (two-gradation) image signal can be displayed on the row scan type display by the employment of a simple arrangement in which the binary image signals of one horizontal scanning line are applied in serial to a shift register and the contents of respective stages of the shift register are provided in parallel for simultaneously driving respective column drive lines of the display (source buses in the case of the liquid crystal display). Accordingly, the signal processing is digital, and hence is very simple. In the past, however, there have not been provided any method and apparatus by which multi-gradation image signals are displayed with three or more gradations on the two-gradation display panel through digital processing.